Subaquatic structure

ABSTRACT

A device for protecting a structure having a foot which rests on the bed of the sea or a like body of water, to prevent undermining of the bed by movements of water at the foot of the structure, comprising a caisson integral with the structure around the foot and having an outer wall and a multiplicity of holes therethrough. Water flows in an average direction towards the inside of the caisson through the lower holes and towards the outside through the upper holes. The holes can be plugged releasably to form a buoyant caisson during construction of the structure.

United States Patent Lamy 5] Oct. 28, 1975 1 SUBAQUATIC STRUCTURE 3,280,569 10/1966 Wosenitz 61/4 3,383,869 5/1968 .larlan 61/3 X [75] Imam Jacques Edward Lamy 3,386,250 6/1968 Katayama... 61/3 FOMQYIaY-aHX-ROSeS, France 3,585,801 6/1971 Koehler 61/465 3,605,416 9/1971 Kubasta 61/465 [73] Asslgnee' Dons Pans France 3,738,113 6/1973 Madary et a1 61/465 [22] Filed: Apr. 16, 1974 [21] Appl. No.1 461,347 Primary ExaminerPhilip C. Kannan Related Us. Application Data Attorney, Agent, or FirmWigman & Cohen [63] Continuation-in-part of Ser. No. 391,465, Aug. 24, 1973, Pat. No, 3,878,684, which is a continuation-impart of Ser. No. 358,500, May 9, [57] ABSTRACT 1973, Pat. No. 3,846,988.

A devlce for protecting a structure having a foot [30] Foreign Application Priority Data which rests on the bed of the sea or a like body of wa- S 5 972 F ter, to prevent undermining of the bed by movements eptt 1 rance of water at the of the structure, comprising a Cais son integral with the structure around the foot and C I having an outer wall and a multiplicity of holes there- [58] 61/3 5 37 through. Water flows in an average direction towards o earc the inside of the caisson through the lower holes and towards the outside through the upper holes. The holes can be plugged releasably to form a buoyant [56] uNlTE g gr z lis gz rENTs caisson during construction of the structure.

3,128,604 4/1964 Sandberg 6l/46.5 7 Claims, 3 Drawing Figures U.S. Patent Oct.28,1975 sheetzofz 3,914,947

SUBAQUATIC STRUCTURE This is a Continuation-in-Part of my copending US. Pat. application Ser. No. 391,465, filed Aug. 24, 1973, now US. Pat. No. 3,878,684, which is a continuationin-part of application Ser. No. 358,500, filed May 9, 1973, now U.S. Pat. No. 3,846,988.

The present invention concerns the construction of structures designed to rest upon the bed of a body of water, particularly towers intended for the exploitation of submarine petroleum deposits.

The invention concerns the protection of the foot of the structure against undermining by currents. It also renders easier towing of the structure by floatation, towards its finishing place or towards the place where it is to be set up, when the structure has been built on land.

According to the invention there is provided a structure for resting upon the bed of a body of water, wherein the foot of the structure comprises a caisson at its periphery, forming a part of the structure and whose outside wall adjacent to the foot is provided with distributed holes which allow the passage of water.

These holes may be formed in such a manner as to be capable of being easily plugged so that, during the passage by water between the place of construction and the place of finishing or of erection, the caisson is kept empty of water and performs the function of a float.

The upper part of the caisson may be closed by a wall, advantageously, by a perforated wall, or can remain open.

The foregoing and further featuresof the invention may be more readily understood from the following description of a preferred embodiment thereof, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a view in elevation and in vertical section of a tower intended to support a platform for working submarine deposits, from above the surface of the water.

FIG. 2 shows, to a larger scale and in section, one advantageous form of the section through a hole, and of a means for plugging this hole.

FIG. 3 shows a detail viewed in the direction of the arrow F of FIG. 2.

FIG. 1 shows a tower, made in reinforced concrete, preferably in prestressed concrete, resting by its foot upon the bed lot the sea and whose top is situated at a certain height h, of the order of a few tens of metres for example, above the mean level 2 of the sea.

The platform and other fixed installations at the top of the tower have not been shown.

Surrounding the foot of the tower there extends a caisson 3 whose volume is completely separated from the interior volume of the tower by an impermeable wall 4. This caisson 3, which forms an integral part of the construction of the tower and whose base is consti tuted by the floor 5 of the tower, consists in the example illustrated, of a vertical wall, 6 and a slanting top wall 7. In other embodiments, this top wall could be horizontal. r

The volume of the caisson is completely submerged below the level 2.

The caisson 3 which forms a projection surrounding the lower part or foot portion of the tower can have, for example, a height 11 of the order of m for a mean dimension of the level 2 of the order of 100 m.

The entire assembly can be a body of revolution about the vertical line X-.-X'.

The wall 6, adjacent to the foot, is pierced by a large number of holes 8 distributed over the entire surface of this wall and having a mean diameter of the order of 0.8m to l m, for example, for a spacing between the hole centres of the order 1.5 m.

The upper wall 7, slanting or horizontal, is also pierced by holes 9, the distribution of which can be the same as that of the holes 6, though this condition is not essential, as the wall 7 may also contain a few large holes only.

Due to the presence of the holes 8 which extend as far as the floor of the structure, this floor is protected against undermining by currents.

In fact, in accordance with the disclosures in my above-mentioned copending US. application Ser. No. 391,465 filed Aug. 24, l973, deep currents which may result from surface swell or from other causes, produce an average unidirectional circulation of water, such that water tends, on average to enter the caisson through the holes 8, adjacent to the foot, whilst it tends, on average, to leave the caisson through the holes 8 located in the upper part of the wall 6 and through the holes 9 in the top wall 7.

In this way, silt or shifting sand displaced by the water tends to approach the caisson 3 at the level of the foot.

In order to encourage this effect, the holes 8 preferably have, instead of simple cylindrical form, a form like that indicated in the above referred to patent application, such that water passing towards the inside of the caisson, in the lower part of the latter, and escaping from the caisson into a region at a higher level, is subject to a pressure drop which is smaller than that for flow in the opposite direction.

The holes 8 may also have a form which converges from the outside towards the inside of the caisson 3 with aslope in section such that when water passes from the inside of the caisson 3 towards the outside, the streams of water separate from the walls of the hole with the formation of turbulence, thus producing a pressure drop. 7

For example, in the case of holes of simple conical form, the cone apex angle may have a value between 25 and 45, preferably between 34 and 38.

The holes may also have a convergent-divergent form as shown in FIG. 2. In this case, supposing the open sea to be on the left of FIG. 2 and the inside of the caisson on the right, the divergent section 11 will have a rather small sloping section, so that in passing from left to right, the stream of water accelerated in the convergent section 10 will be simply decelerated in the divergent section 11, without separation, and therefore with a low pressure drop. On the other hand, the section 10 of the hole, when functioning as a diverging passage with flow from right to left, will have a rather steep gradient in section, producing separation and turbulence, generating pressure drop. 7

If the section 10 is of simple conical form, the cone apex angle should then be between the numerical limits indicated above, whilst for the section 11, the cone apex angle should generally be less than 10.

Other forms of hole are equally possible to obtain low pressure drop in passing from the outside to the inside of the caisson and a high pressure drop inthe opposite direction.

The holes 9 in the top wall 7 can have any form since they serve only for the circulation of water, being situated remotefrom the floor of the structure.

Thus, the wall 7 may, in certain applications comprise one large hole instead of a number of holes distributed like the holes 8 in the wall 6 adjacent to the foot. The holes in the wall 7 may also be convergent upwards (conical), so as to facilitate the escape of water and hinder its entry into the caisson. In another embodiment (not shown) the top wall 7 may be omitted.

The caisson 3 can be non-continuous and can be subdivided into elements by walls, which may be radial for example, for the purpose of strengthening the structure.

When, after the construction of the structure has begun in a dock or basin on shore, for example in an excavation which can be flooded by the sea, it is desired to move the structure by floatation to a site for finishing, the holes 8 and possibly 9 are first plugged, so as to close the caisson 3 watertight, at least until floatation, and to keep it empty of water in this way.

The caisson 3 which is formed on the perimeter of the foot of-the structure thus serves as a float, the assembly being designed and, where required, ballasted in such a manner as to obtain the desired stability in floating.

The subdivision of the caisson 3 by radial walls gives a system of partitioning which provides security against local water leakage.

- Combined with this caisson 3, there can be an arch 12 at the base of the structure, which retains air in the form of a large bubble, when launched into the water, thus contributing to the buoyancy.

This arch will advantageously take the form of a spherical dome with its centre on the vertical centre line XX' of the structure.

By arranging the caisson 3 around the springing of this dome, a simple and economical form of construction is obtained for the foot part of the structure, at the sametime as good buoyancy.

In certain cases, the caisson 3 could also be made use of (by plugging all the holes 8 and 9 in the walls 6 and 7) as could also possibly the dome 12, to confer (or to contribute to) the buoyancy necessary for the finished structure to be towed to its place of erection.

FIGS. 2 and 3 show an example of the plugs. They consist of a plate 13, of steel for example, which can be housed in a rebate 14 provided at the outer end of a hole and-co-operating with a plastic joint-member 15 which may be cemented, for example, to the inside face of the plate 13. This inside face is also provided with projections 13a adapted to the shape of the walls 10 of the hole, in such a manner as to centralize the plate effectively. This latter is held in place by a tie-rod 16 attached to the plate 13 and passing through a bar 17 which can be placed diametrally across the inner opening of the hole into the caisson. The attachment of the tie-rod 16 to the bar 17 can be made in any convenient manner, for example by a taper key 18 which can be readily disassembled. It is advantageous for the bar 17 to be resilient, such that the tie-rod 16, of suitable length, may be kept under tension when the key 18 is fitted. Diametrally opposite recesses 19 can be provided in the concrete so as to locate the position of the bar 17.

Variations of this type of device can naturally be realized.

Once the structure has arrived at its place for finishing or erection, the plugs are removed from the holes 8 and 9 so as to allow the caisson to fill, the air which it holds escaping through the holes 9 in its top wall. At the same time, the air contained in the dome 12 is allowed to escape through pipes 24, opening out at the top of the structure and which were plugged until that time. The structure being ballasted in this way, its buoyancy is removed and it comes to rest upon the sea bed where it can be anchored.

The drawing also shows a chamber 20 at the upper part of the structure, which comprises an impermeable floor 21 and whose side-walls 22 are provided with holes 23, regularly divided between either side of the mean level 2 of the water. These perforated walls have as their purpose the dissipation of the energy of the surface swell, and the reduction of the forces exerted on the structure, in accordance with a previously known technique.

I claim:

1. A structure having an integral foot caisson which is designed for resting upon the bed of a body of water and which comprises an outer peripheral ported wall having a multiplicity of holes formed therethrough for the passage of water, wherein the improvement comprises releasable means for selectively plugging watertightly said holes to prevent transiently such passage of water therethrough, said releasable means comprising a plate adaptable to a first opening of a hole, a tie-rod attached to said plate, an anchor-member adaptable across a second opening of said hole opposite said first opening thereof, and means for releasably fastening said anchor'member to said tie-rod to exert a tensile force on said tie-rod.

2. A structure as claimed in claim 1, wherein said foot caisson further comprises a top ported wall having a multiplicity of further holes formed therethrough for the passage of water and connecting said outer peripheral ported wall to the main body portion of the structure, and further releasable means for selectively plugging watertightly said further holes to prevent transiently such passage of water therethrough, said further releasable means comprising a further plate adaptable to a first opening of a further hole, a further tie-rod attached to said further plate, a further anchor-member adaptable across a second opening of said further hole opposite said first opening thereof, and further means for releasably fastening said further anchor-member to said further tie-rod to exert a tensile force on said further tie-rod.

3. A unitary integrated structure designed for resting upon the bed of a body of water in an upright position such as to present a head section emerging above the water level and overtopping a submerged foot section integral therewith, said foot section comprisng an upper columnar body extending downwardly from said head section below said water level and ending with a lower annular coffer-like base which comprises a generally upright inner solid wall portion, a floor portion formed of a continuous slab extending radially all around said wall portion and integral therewith, said slab being designed for engaging through its undersurface said water bed to seat said structure thereon, and an outer peripheral ported wall projecting upwards from and intergral with said slab to surround said inner solid wall portion in radially spaced relationship therewith and to bound an annular caisson integral with the structure and bottomed by said slab, said outer peripheral ported wall having a height which is but a minor fraction of the depth of the body of water whereby the entirety of said outer peripheral ported wall is deeply submerged when said unitary integrated structure is seated by means of said slab on said water bed.

4. A structure as claimed in claim 3, wherein said outer peripheral ported wall presents a multiplicity of holes formed therethrough for the passage of water and designed with a hydrodynamic outline such as to produce a smaller pressure drop when transversed by water flowing from the outside to the inside of said caisson, than in the opposite direction, that is from the inside to the outside of said caisson.

5. A structure as claimed in claim 4, wherein said holes comprise at least one section which converges from the outside towards the inside of the caisson and which exhibits a sufficiently steep convergence to ensure that water flowing from the inside to the outside of said caisson through said holes separates from their wall. r 1

6. A structure as claimed in claim 3, further comprising mechanically controllable and optionally releasable valve means for selectively plugging watertightly said holes to prevent transiently such passage of water therethrough so long as said valve means are not voluntarily released from said holes.

7. A structure as claimed in claim 5, wherein said releasable plugging means comprise a plate adaptable to a first opening of a hole, a tie-rod attached to said plate, an anchor-member adaptable across a second opening of said hole opposite said first opening thereof, and means for releasably fastening said anchor-member to said tie-rod to exert a tensile force on said tie-rod. 

1. A structure having an integral foot caisson which is designed for resting upon the bed of a body of water and which comprises an outer peripheral ported wall having a multiplicity of holes formed therethrough for the passage of water, wherein the improvement comprises releasable means for selectively plugging watertightly said holes to prevent transiently such passage of water therethrough, said releasable means comprising a plate adaptable to a first opening of a hole, a tie-rod attached to said plate, an anchor-member adaptable across a second opening of said hole opposite said first opening thereof, and means for releasably fastening said anchormember to said tie-rod to exert a tensile force on said tie-rod.
 2. A structure as claimed in claim 1, wherein said foot caisson further comprises a top ported wall having a multiplicity of further holes formed therethrough for the passage of water and connecting said outer peripheral ported wall to the main body portion of the structure, and further releasable means for selectively plugging watertightly said further holes to prevent transiently such passage of water therethrough, said further releasable means comprising a further plate adaptable to a first opening of a further hole, a further tie-rod attached to said further plate, a further anchor-member adaptable across a second opening of said further hole opposite said first opening thereof, and further means for releasably fastening said further anchor-member to said further tie-rod to exert a tensile force on said further tie-rod.
 3. A unitary integrated structure designed for resting upon the bed of a body of water in an upright position such as to present a head section emerging above the water level and overtopping a submerged foot section integral therewith, said foot section comprisng an upper columnar body extending downwardly from said head section below said water level and ending with a lower annular coffer-like base which comprises a generally upright inner solid wall portion, a floor portion formed of a continuous slab extending radially all around said wall portion and integral therewith, said slab being designed for engaging through its undersurface said water bed to seat said structure thereon, and an outer peripheral ported wall projecting upwards from and intergral with said slab to surround said inner solid wall portion in radially spaced relationship therewith and to bound an annular caisson integral with the structure and bottomed by said slab, said outer peripheral ported wall having a height which is but a minor fraction of the depth of the body of water whereby the entirety of said outer peripheral ported wall is deeply submerged when said unitary integrated structure is seated by means of said slab on said water bed.
 4. A structure as claimed in claim 3, wherein said outer peripheral ported wall presents a multiplicity of holes formed therethrough for the passage of water and designed with a hydrodynamic outline such as to produce a smaller pressure drop when transversed by water flowing from the outside to the inside of said caisson, than in the opposite direction, that is from the inside to the outside of said caisson.
 5. A structure as claimed in claim 4, wherein said holes comprise at least one section which converges from the outside towards the inside of the caisson and which exhibits a sufficiently steep convergence to ensure that water flowing from the inside to the outside of said caisson through said holes separates from their wall.
 6. A structure as claimed in claim 3, further comprising mechanically controllable and optionally releasable valve means for selectively plugging watertightly said hOles to prevent transiently such passage of water therethrough so long as said valve means are not voluntarily released from said holes.
 7. A structure as claimed in claim 5, wherein said releasable plugging means comprise a plate adaptable to a first opening of a hole, a tie-rod attached to said plate, an anchor-member adaptable across a second opening of said hole opposite said first opening thereof, and means for releasably fastening said anchor-member to said tie-rod to exert a tensile force on said tie-rod. 